Properties of casein

Formolised casein is a rigid hom-like material which may be made available in a wide variety of colours and patterns. By common consent it is recognised as having a pleasant feel and appearance and it is properties which are relevant to current commercial application. 

Mechanical properties are typical of a rigid plastics material and numerical values (Table 30.2) are similar to those for poly(methy 1 methacrylate). Although thermosetting, it has a low heat distortion temperature ( 80°C) and is not particularly useful at elevated temperatures. 

When dry, casein is a good electrical insulator but is seriously affected by humid conditions. For this reason it can no longer compete with the mcuiy alternative plastics materials now available for electrical applications. 

Both acids and alkalis will adversely affect the material. Strong alkalis and acids will cause decomposition. The water absorption is high and consequently casein is easily stained. As a corollary to this it may be dyed without difficulty. Acidic and basic water-soluble dyes are normally used. Typical properties of casein plastics are given in Table 30.2. 

The use of casein plastics was severely curtailed with the development of synthetic polymers, particularly after the Second World War. In addition stricter regulations concerning health and safety at work will have caused attention to be drawn to the formolising process. In the experience of the author the environment surrounding the formolising baths is most unpleasant and this will have accelerated the demise of the casein manufacturing industry. 

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Chemical nature Isolation of casein from milk Production of casein plastics Properties of casein Applications Miscellaneous Protein Plastics Derivatives of Natural Rubber Gutta Percha and Related Materials Shellac... 

Caseins are the major proteins in bovine milk and about 95% of the caseins exist as casein micelles. The structure and properties of casein micelles influence a wide range of technological uses of milk. Light microscopy, SEM, and TEM have been frequently used to study casein... 

Helstad, K. M., Bream, A. D., Trckova, J., Paulsson, M., and Dejmek, P. (2005). Nano-heological properties of casein. In "Food Colloids Interactions, Microstructure and Processing", (E. Dickinson, Ed.), pp. 218-229. The Royal Society of Chemistry, Cambridge. 

But we must appreciate how the phosphate group acts much like the anion from a weak acid (see Chapter 6), so its exact composition will depend on the pH of solution. The pH of cow s or human milk is about 7 (see Table 6.4). If the pH decreases much below about 6 (e.g. by adding an acid in the form of orange juice), the phosphates become protonated. The emulsifying properties of casein cease as soon as its structure changes, causing the milk to separate. 

Dickinson, E., Semenova, M.G., Antipova, A.S., Pelan, E. (1998). Effect of high-methoxy pectin on properties of casein-stabilized emulsions. Food Hydrocolloids, 12, 425 432. 

McGann, T.C.A., Fox, P.F. (1974). Physico-chemical properties of casein micelles reformed front urea-treated milk. Journal of Dairy Research, 41, 45-53. 

Emulsification properties in model food systems. Pearson et al. (25) investigated the emulsification properties of caseinate and NFDM in model emulsion systems produced by blending soybean oil into an aqueous buffer system as a function of pH and ionic strength (Figures 7 and 8). They found that caseinate exhibited good emulsification properties under all pH and ionic strength conditions studied, but was particularly effective at pH 10.4. 

The ageing at 5°C of whippable emulsions such as ice cream mix will enhance the hydration of milk proteins in the system. This is due to a property of casein micelles in milk. At low temperatures, the hydration or voluminosity of casein increases. The voluminosity is the volume of hydrated protein per gram of protein. This can be studied by analyzing the protein and water content in the sedimented casein pellet after centrifugation of skimmed milk. 

Enzymatic hydrolysis modifies the foaming properties of casein. Protamex hydrolysates of sodium caseinate (DH 0.5 and 1.0%) displayed increased foam expansion at pH 2, 8 and 10 as compared with unhydrolyzed caseinate (Slattery and FitzGerald, 1998). Hydrophobic peptides resulting from... 

Chobert, J.-M., Sitohy, M.Z., and Whitaker, J.R. 1988a. Solubility and emulsifying properties of caseins modified enzymatically by Staphylococcus aureus V8 protease. J. Agric. Food Chem. 36, 220-224. 

Medina, A.L., Colas, B., Le Meste, M., Renaudet, I., and Lorient, D. 1992. Physicochemical and dynamic properties of caseins modified by chemical phosphorylation. J. Food Sci. 57, 617-620. 

Some physical and functional properties of casein modified by the covalent attachment of amino acids are given in Table IX. Despite extensive modification, the relative viscosities of 2% solutions of the modified proteins did not change significantly, with the exception of aspartyl casein which was more viscous. There was some decrease in the solubilities of aspartyl casein and tryptophyl casein as compared with the casein control. It is anticipated that adding some 11.4 tryptophyl residues per mole of casein would decrease the aqueous solubility of the modified protein. However the results with aspartyl casein are unexpected. The changes in viscosity, solubility, and fluorescence indicate that aspartyl casein is likely to be a more extended molecule than the casein control. There was a marked decrease in the fluorescence of aspartyl casein and tryptophyl casein (see Table IX). The ratios of the fluorescences of acetylmethionyl casein to methionyl casein and t-BOC-tryptophyl casein to tryptophan casein were 1.20 and 2.01, respectively, indicating the major effects that these acyl groups have on the structure of the casein. 

Table IX. Some Physical Properties of Casein Modified by Covalent Attachment of Some Amino Acids0...

Dickinson, E. 1989 Surface and emulsifying properties of caseins. J. Dairy Res. 56, 471-477. Goff, H.D., Liboff, M., Jordan, W.K., Kinsella, J.E. 1987. The effects of polysorbate 80 on the fat emulsion in ice cream mix evidence from transmission electron microscopy studies. Food Microstruct. 6, 193—198. 

Table III. Physico-Chemical Properties of Casein Micelles in Milka... 

Bazinet L, Gendron C, Ippersiel D, Rene-Paradis J, Tetreault C, Beaudry J, Britten M, Mahdavi B, Amiot J, and Lamarche F. Effect of type of added salt and ionic strength on physicochemical and functional properties of casein isolates produced by electroacidification. J Agric. Food Chem. 2002 50(23) 6875-6881. 

Ethers. Methylation. The simplest ether is the methyl ether. Reaction of wood with dimethyl sulfate and NaOH (54, 55), or methyl iodide and silver oxide (54) are two systems that have been reported. Methylation up to 15% weight gain did not affect the adhesive properties of casein glues. The mechanical properties of methylated wood are greatly reduced because of the severe reaction conditions required. 

Sandra, S. and Dalgleish, D. G. (2005). Effects of ultra-high-pressure homogenization and heating on structural properties of casein micelles in reconstituted skim milk powder. Int. Dairy ]. 15,1095-1104. 

Table 30.2 Some physical properties of casein plastics...

Schorsch et al. (2001) examined the effects of denaturation of whey proteins in the presence and absence of casein micelles on gel properties. Heat treatment sequence was found to influence the acid gelation properties of casein-whey mixtures. Denaturation of whey proteins in the absence of casein micelles induced more rapid gelation on addition of acid. Gels made from these milks had a more particulate gel structure than gels made from casein-whey mixtures which were heated without prior denaturation of the whey proteins. 

Oliver, C.M., Melton, L.D., and Stanley, R.A. (2006b). Functional properties of caseinate glycoconjugates prepared by controlled heating in the dry state. ]. Sci. Food Agric. 86, 732-740. 

Table 1 Functional Properties of Casein and Enzymatically Modified Proteinsab...

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